1. Field of the Invention
The invention pertains to the field of the generation of a plasma which is a highly ionized gas. More in particular, the invention pertains to the use of a plasma as a heat source in the smelting and refining of metal material. The field of the invention includes the apparatus and the method of producing a plasma by the co-action of alternating current and direct current electric fields in the presence of an externally applied axial magnetic field. As referred to herein, the invention pertains to a method and apparatus for generating a magneto-plasma.
The fields of arts to which the invention pertains also includes a method and apparatus for smelting and refining metal material during passage of the material through a magneto-plasma. The field of the invention also includes the control of the length and lateral cross-section of the magneto-plasma as well as the stable operating conditions of input power and temperature.
2. Description of the Prior Art
Throughtout the history of the metal producing and fabricating industries, attempts have been made to recover metal from scrap material. The two major types of scrap metal material are revert scrap and purchased commercial grade scrap. Revert scrap material is scrap which unavoidably results from metal-making and finishing operations. Purchased commercial grade scrap includes prompt industrial scrap and dormant scrap. Industrial scrap which is a by-product of metal fabricating and forming industries in manufacturing their products comprises prompt industrial scrap. Dormant scrap comprises obsolete, worn-out, or broken products of consuming industries. Revert scrap and prompt industrial scrap can usually be identified easily as to source and composition and thus it is more valuable for metal recovery. Dormant scrap requires careful sorting and classification to prevent the contamination of metal in the furnace with unwanted chemical elements from alloys that may be present in such scrap.
When the chemical compositions of scrap is known, the scrap can prove to be a valuable source of alloying elements needed in the steel industry for the production of alloy steels. Full advantage is taken of this source in the production of alloy steels in electric furnaces (electric arc, induction, etc.) as well as in the basic oxygen furnace and the open-hearth furnace, because the preponderance of production consists of carbon and low-alloy steels.
Unidentified alloying elements in scrap can be a source of trouble. Tin, copper, nickel and other elements present in scrap can alloy readily with steel and, in many instances render it unfit for its intended use. Relatively small amounts of these metals can contaminate an entire heat of steel. Tin and copper in certain amounts can cause brittleness and bad surface conditions in steel. Nickel and tin not only contaminate heats into which they may be unintentionally introduced, but may deposit a residue in the furnace that is absorbed by successive heats with resultant contamination. Lead is extremely harmful to furnace bottoms and refractories, and if present in sufficient quantities, may cause the furnace to fail by penetrating joints or cracks in the bottom to form channels through which molten steel may flow. Therefore, even with purchased clean commercial grade metal scrap, it is extremely important that it be sorted before being used.
Metal scrap may be that separated from solid waste material. Due to the miscellaneous nature of solid waste material, a large percentage of it is of unknown origin and composition. It is obviously uneconomical and impractical to analyze chemically each individual piece of scrap in the huge amounts of metal scrap present in solid waste material. As a result up to now, it is the usual practice for the great majority of municipal governments to dump all metals with the solid waste material or refuse into a land fill. In certain instances there are relatively small projects which utilize combustible materials from solid-waste for supplemental fuel, and which separate scrap metal from the waste material as a product.
Scrap metal separated from solid-waste may present a difficult technological problem for the steel and aluminum industries. Such scrap metal materials are extremely contaminated by foreign materials on the surface. A cleaning process for removing the contaminants is expensive. In addition, the chemical composition of such scrap metal is unknown. Moreover, when the scrap includes steel containers another problem arises since tin-plated steel and tin are not acceptable in steel alloys. If the scrap includes aluminum containers, the lids of the containers are made from a different alloy than the bodies. Thus it can be seen that the utilization of this kind of scrap metal for electric-arc furnaces, induction furnaces, basic oxygen furnaces and open-hearth furnaces of the steel industry can be uneconomical and impractical. The same can be said for the aluminum industry. The lid and body may contain about 2.25 percent magnesium and 1 percent manganese on the average. Both elements are usually undesirable in secondary aluminum alloys. To remove magnesium and dilute the manganese content are costly. As a result, less than 2 percent of clean aluminum containers can be recycled today. Almost none of contaminated aluminum containers are being recycled today. Therefore, the utilization of this kind of scrap metal for electric-arc furnaces, induction furnaces, basic oxygen furnaces, open-hearth and aluminum alloy industry is uneconomical and impractical.
After a costly cleaning process, contaminated steel scrap in small quantities can be introduced into a blast furnace. Thus the blast furnace can utilize a small proportion of contaminated steel scrap in conjunction with approximately 93 percent or more of iron-bearing materials (i.e., iron ore) to produce pig iron or hot metals; however, there are limitations in utilizing this kind of steel scrap. Not only is a blast furnace limited to a small portion of scraps but also a blast furnace must be located near to a source of iron ore and coke. The required location of a blast furnace can therefore mean transportation expenses for handling scraps which can be prohibitive if the distances involved are outside of an appropriate one hundred mile radius of the blast furnace. Therefore, these limitations cause steel scrap separated from solid-waste to have a very low economic value where moderate distances to a blast furnace are involved and virtually no economic value where large distances are involved.
The prior art includes methods and apparatus for the use of an electric arc as well as a plasma in refining metal materials.
U.S. Pat. No. 3,546,348 which issued to Serafino M. Decorso on Dec. 8, 1970 discloses a vacuum furnace for purifying or refining metal materials when heated by an electric arc.
U.S. Pat. No. 3,201,560 which issued to R. F. Mayo et al on Aug. 17, 1965 discloses an arc discharge device for generating high temperature gas. The patent discloses the use of a high intensity magnetic field directed axially with respect to the chamber through which the arc region extends. The interaction between the electric field of the arc electrodes and the transverse magnetic field creates a force which is perpendicular to these vector quantities and which acts upon the current carriers of the arc. As a result, a curvilinear motion is imparted to the current carriers. The presence of the high intensity fields increases arc defusion and results in a positive effective resistance characteristic of the arc. This is in direct contrast to a normal arc which has a negative resistance characteristic.
U.S. Pat. No. 2,960,331 which issued to C. W. Hanks on Nov. 15, 1960 discloses the use of an electric arc in refining metal particles which are converted into molten droplets by the arc. The system operates within an evacuated chamber.
U.S. Pat. No. 3,429,691 which issued to W. J. McLaughlin on Feb. 25, 1969 discloses the use of a hydrogen plasma to reduce titanium dioxide to titanium metal by passing finely divided titanium dioxide particles through the plasma. A winding surrounding the plasma generator provides a magnetic field for controlling the plasma velocity.
U.S. Pat. No. 3,536,885 which issued to P. Mitchell on Oct. 27, 1970 discloses a plasma torch in which a pilot gas plasma is formed between direct current electrodes and the resulting plasma is directed to a plasma region extending between alternating current electrodes.
U.S. Pat. No. 3,248,513 which issued to J. A. F. Sunnen on Apr. 26, 1966 also shows a plasma device in which a plasma formed between direct current electrodes is extended to a region formed by alternating current electrodes.